A density-functional study of van der Waals forces: rare gas diatomics

Various exchange-correlation functionals are tested by calculating potential energy curves of six rare gas diatomic molecules: He2, Ne2, Ar2, HeNe, HeAr, and NeAr. The local density approximation (LDA) severely overestimates the dissociation energies, while the ‘half-and-half’ functional of Becke displays very weak binding. Two other functionals based on the generalized gradient approximation (GGA) give repulsive potential energy curves with no minimum.